Vet Times The website for the veterinary profession https://www.vettimes.co.uk TAPEWORM INFECTION IN HORSES Author : Rachael Conwell Categories : Vets Date : November 1, 2010 Rachael Conwell looks at the three species of equine tapeworm and considers the most appropriate treatments THREE tapeworm species have been identified in the horse; Anoplocephala perfoliata is the most common and pathogenic 1, while Anoplocephala magna and Paranoplocephala mamillana are considered rare 2. The adult tapeworm is approximately 4cm to 8cm long and attaches to the mucosa at the ileocaecal junction of the gastrointestinal (GI) tract. The tapeworm has an indirect life cycle. Oribatid mites are the intermediate host and occur in high densities on uncultivated pastures, acting as a reservoir of infective stages following tapeworm egg ingestion in infected horse faeces 3. Horses subsequently ingest mites containing the infective cysterceroid stages in hay or when grazing pasture. The worms develop on the mucosal lining and mature to adults, shedding eggs to complete the life cycle. This takes between four and six months. Tapeworm infections in horses are relatively common in the UK 4. Variable levels of prevalence, based on abattoir surveys, have been identified throughout Europe, with infection rates of up to 69 per cent of horses in England and Wales and 51 per cent in Ireland 5. Horses of all ages can be infected. Based on serological evaluation, peak infection intensity has been identified in both younger (0.5 to two years) and older (more than 15 years) animals, with a plateau between three and 15 years 6. 1 / 6
Significance of tapeworm Equine tapeworm infection used to be considered of little clinical significance, especially in comparison to the large and small strongyles. However, peritonitis, caecal rupture, ileal impaction, spasmodic colic, and ileocaecal, caecocolic and caecocaecal intussusceptions have all been linked to tapeworm infection 3, 7, 8, 9. An abattoir study found a significant correlation between parasite burden and grading of histopathological lesions in the mucosa and submucosa at the ileocaecal junction 10. Horses infected with high numbers of tapeworm had erosive-ulcerative lesions, with severe, deep, mixed inflammation extending to muscle layers. There was also significant reduction in myenteric plexi and neuronal cells in parasitised horses, which could impair intestinal motility 10. Parasite burden is a risk factor for colic 8. Although numerous management factors can be associated with colic, spasmodic colic has been linked with A perfoliata, detected both coprologically 7 and serologically 9. Conversely, there was no significant association between colic and strongyle egg count. Ileal impactions have also been associated with tapeworm infection in the UK 9. A study in the south-eastern USA identified failure to administer a pyrantel salt in the three months before hospital admission as a risk factor for development of ileal impaction, also supporting the role of A perfoliata 8 in this. Diagnosis Diagnosis by coprological examination is limited by the shedding of low numbers of eggs in the faeces. The McMaster technique, which is used for detection of nematode eggs, has a very low sensitivity for tapeworms11. Sedimentation/flotation techniques have a better sensitivity at 54 to 61 per cent, but are limited to specialist labs and rarely used in practice as they are messy, timeconsuming and lack sensitivity 6. The sensitivity of coprological examination for cestode eggs is increased by greater numbers of adult worms (up to 89 per cent if more than 20 tapeworms are present) 5. Administration of an anti-cestode treatment can increase the number of tapeworm eggs in the faeces due to tapeworm death, detachment from the intestinal wall and degeneration of the proglottid, thus releasing eggs 1. The optimum time to collect faeces for cestode eggs is one day posttreatment. However, this only provides a retrospective indication of tapeworm burden and is not a prospective measure to determine whether to treat. The development of an enzyme-linked immunosorbent assay (ELISA) in the 1990s identified a correlation between the intensity of infection and the level of serum IgG (T) for a 12/13kDa excretory/secretory protein of A perfoliata 12. The values are reported as optical density (OD). OD values of 0.000 to 0.200 are classed as zero/low infection intensity, 0.201 to 0.600 as moderate and greater than 0.600 as high infection intensity. A diagnostic sensitivity of 68 per cent and 2 / 6
specificity of 95 per cent were reported 12. Much research in this area has followed, and found the tapeworm ELISA has considerable variation in antibody levels between individual horses with similar tapeworm burdens5 and a lack of sensitivity and specificity to recent changes in parasite status 13. High background levels of antibodies to A perfoliata were found in horses with no physical evidence of tapeworm in a Danish abattoir study (false positives) 14. However, the anthelmintic use in the months prior to submission to the abattoir was not known, and it is possible microscopic immature stages may have been missed, resulting in a persistently high ELISA OD. Serology may, therefore, be most useful for identifying exposure rather than current infection due to persistence of the antibodies 7. A decline in antibody levels is observed after treatment but can vary between individuals 3. This may be as a result of horses previously exposed to A perfoliata but no longer actively infected, or due to variability in the parasite-induced immune response and rate of decay of circulating antibody 15. Anthelmintic history is, therefore, needed to fully interpret the tapeworm ELISA 11. Research has investigated the development of a coproantigen test 15, 16. Coproantigen tests detect parasite antigen in the faeces and are most useful for parasites that develop fully in the GI tract without a tissue phase. Preliminary studies showed a significant positive response in all the known infected horses and a very low OD in the controls. This could potentially be useful to identify current infection status, monitor response to treatment and possibly identify resistance development. An abattoir study of more than 400 horses in Canada found coproantigenic ELISA had 74 per cent sensitivity and 92 per cent specificity and a positive correlation between antigen concentration and tapeworm intensity, although overall cestode prevalence was low at seven per cent and most horses had fewer than 30 tapeworms 15. A study compared a faecal polymerase chain reaction (PCR) assay with coprological and serological tests, and the ability to detect the presence and absence of tapeworm DNA posttreatment 13. The high sensitivity of the PCR meant false negatives were unlikely, but it did not provide an estimate of parasitic burden. Failure to detect horses carrying few worms is probably less important than the ability to detect those with large burdens 4. Treatment Traditionally, recommendations to owners have been twiceyearly treatment with either pyrantel embonate or praziquantel. Targeted strategic therapy is now promoted in a bid to reduce the rate of resistance development 11. This entails only treating horses that have a significant tapeworm burden. In Denmark, anthelmintic use is based on a diagnosis by a veterinary surgeon and restricted to prescriptiononly drugs, to attempt to reduce anthelmintic resistance development. A 3 / 6
Danish study suggested horses with an ELISA OD equal to or greater than 0.7 should receive anticestode treatment 5. A nematocidal dose of 6.6mg/ kg pyrantel embonate has partial cestocidal activity versus A perfoliata at approximately 70 per cent. This increases to 93 to 100 per cent efficacy when used at double the dose (13.2mg/kg) 17. A dose of 1mg/kg praziquantel is highly effective (greater than 98 per cent) in elimination of A perfoliata 18 and also of the other, less commonly found, tapeworm species 2. Pyrantel acts as a depolarising neuromuscular blocker, paralysing the worm and causing it to be expelled intact. Praziquantel causes irreversible focal vacuolisation with disintegration of the cestodal tegument. Suspected host anaphylactic reaction to subsequently released parasite antigen may result in colic and diarrhoea if there is a high tapeworm burden 17 and recent administration of anthelmintics is a recognised risk factor for colic and diarrhoea 19. An investigation of 14 horses reported with mild colic and diarrhoea, within eight to 12 hours postdosing with a combination anthelmintic (praziquantel and ivermectin) identified 10 (71 per cent) with a high tapeworm infection intensity (OD greater than 0.6) 19. Pyrantel may be indicated in treatment of horses with a poor de-worming history and high ELISA OD, where an increased risk of post-treatment colic and diarrhoea is present. Using a single dose to remove part of the tapeworm burden, followed by praziquantel two weeks later, is a useful option (Proudman C J, personal communication). No tapeworm resistance to praziquantel or pyrantel has yet been reported. The optimal time for blood sampling to monitor for tapeworm is suggested as four to five months post-treatment to minimise the influence of antibody persistence 3. The rate of ELISA OD decline may be more rapid if horses are put on clean pasture after treatment for tapeworm, although this may not comply with current recommendations for control of other parasites, such as the small strongyles. Horses returning to pasture post-treatment, where parasite control is minimal, are likely to have high infection pressure. If using a rising ELISA OD to detect reinfection with A perfoliata, it is suggested that a rise in OD of 0.2 from consecutive samples taken at bimonthly intervals is appropriate 11. References 1. Sanada Y, Senba H and Mochizuki R (2009). Evaluation of marked rise in faecal egg output after biothenol administration and its application as a diagnostic marker for equine Anoplocephala perfoliata infection, J Vet Med Sci 71: 617-629. 2. Rebhun S, Visser, M, Yoon S and Marley S E (2007). Efficacy of a combination 4 / 6
ivermectin/praziquantel paste against nematodes, cestodes and bots in naturally infected ponies, Vet Record 161: 722-724. 3. Abbott J B, Mellor D J, Barrett E J et al (2008). Serological changes observed in horses infected with Anoplocephala perfoliata after treatment with praziquantel and natural reinfection, Vet Record 162: 50-53. 4. Morgan E R, Netzel N, Povah C and Coles G C (2005). Prevalence and diagnosis of parasites of the stomach and small intestine in horses in SW England, Vet Record 156: 597-600. 5. Kjær L N, Lungholdt M M, Nielson M K et al (2007). Interpretation of serum antibody response to Anoplocephala perfoliata in relation to parasite burden and faecal egg counts, Equine Vet J 39: 529-533. 6. Matthews J B, Hodgkinson J E, Dowdall S M J and Proudman C J (2004). Recent developments in research into the cyathostominae and Anoplocephala perfoliata, Vet Res 35: 371-381. 7. Veronesi F, Diaferia M and Piergili Fioretti D (2009). Anoplocephala perfoliata infestation and colics in the horse, Vet Res Commun 33: S161-S163. 8. Little D and Blikslager A T (2002). Factors associated with development of ileal impaction in horses with surgical colic: 78 cases (1986-2000), Equine Vet J 34: 464-468 9. Proudman C J, French N P and Trees A J (1998). Tapeworm is a significant risk factor for spasmodic colic and ileal impaction colic in the horse, Equine Vet J 30: 194-199 10. Pavone S, Veronesi F, Piergili Fioretti D and Mandara M T (2010). Pathological changes caused by Anoplocephala perfoliata in the equine ileocaecal junction, Vet Res Commun 34: S53-S56. 11. Abbott J B and Barrett E J (2008). The problem of diagnosing tapeworm infections in the horse, Equine Vet J 40: 5-6. 12. Proudman C J and Trees A J (1996). Use of excretory/secretory antigens for the serodiagnosis of Anoplocephala perfoliata cestosis, Vet Parasitology 61: 239-247. 13. Traversa D, Fichi G, Campigli M et al (2008). A comparison of coprological, serological and molecular methods for the diagnosis of horse infection with Anoplocephala perfoliata (Cestoda, cyclophyllidea), Vet Parasitology 152: 271-277. 14. Nielson M K, Fritzen B and Duncan J L (2010). Practical aspects of equine parasite control: a review based upon a workshop discussion consensus, Equine Vet J 42: 460-468. 15. Skotarek S L, Colwell D D and Goater C P (2010). Evaluation of diagnostic techniques for Anoplcephala perfoliata in horses from Alberta, Canada, Vet Parasitology 172: 249-255. 16. Kania S A and Reinemeyer C R (2005). Anoplocephala perfoliata coproantigen detection: a preliminary study, Vet Parasitology 127: 115-119. 17. Marchiondo A A, White G W and Smith L L et al (2006). Clinical field trial efficacy and safety of pyrantel pamoate paste (19.13 per cent w/w pyrantel base) against Anoplocephala perfoliata in naturally infected horses, Vet Parasitology 137: 94-102. 18. Holm-Martin M, Levot G W and Dawson K L (2005). Control of endoparasites in horses with a gel containing moxidectin and praziquantal, Vet Record 156: 835-838. 19. Barrett E J, Blair C W, Farlam J and Proudman C J (2005). Postdosing colic and 5 / 6
Powered by TCPDF (www.tcpdf.org) diarrhoea in horses with serological evidence of tapeworm infection, Vet Record 156: 252-253. 6 / 6